closes bpo-27494: Fix 2to3 handling of trailing comma after a generator expression (#3771)

diff --git a/Lib/lib2to3/fixer_util.py b/Lib/lib2to3/fixer_util.py
index babe6cb..2f9b1c2 100644
--- a/Lib/lib2to3/fixer_util.py
+++ b/Lib/lib2to3/fixer_util.py
@@ -101,8 +101,8 @@
         test.prefix = " "
         if_leaf = Leaf(token.NAME, "if")
         if_leaf.prefix = " "
-        inner_args.append(Node(syms.comp_if, [if_leaf, test]))
-    inner = Node(syms.listmaker, [xp, Node(syms.comp_for, inner_args)])
+        inner_args.append(Node(syms.old_comp_if, [if_leaf, test]))
+    inner = Node(syms.listmaker, [xp, Node(syms.old_comp_for, inner_args)])
     return Node(syms.atom,
                        [Leaf(token.LBRACE, "["),
                         inner,
@@ -208,7 +208,7 @@
         next = getattr(next, attr)
 
 p0 = """for_stmt< 'for' any 'in' node=any ':' any* >
-        | comp_for< 'for' any 'in' node=any any* >
+        | old_comp_for< 'for' any 'in' node=any any* >
      """
 p1 = """
 power<